An embolism is a condition where the blood flow in an artery is blocked by a foreign body, such as a blood clot or an air bubble.

To function properly, the body's tissues and organs need oxygen, which is transported around the body in the bloodstream. If the blood supply to a major organ – such as the brain, heart or lungs – is blocked, the organ will lose some or all of its function.

Two of the most serious conditions caused by an embolism are:

  • stroke – where the supply of blood to the brain is interrupted or cut off
  • pulmonary embolisms – when a foreign body blocks the artery transporting blood to the lungs

What causes an embolism?

A foreign body is any object or substance which shouldn't be in your blood. Foreign bodies that cause embolisms are known as emboli – a single emboli is called an embolus.

Blood clots

Blood contains natural clotting agents which help prevent excessive bleeding when you cut yourself.

Certain health conditions – such as obesity, heart disease, cancer or pregnancy – can cause blood clots to form even where there's no bleeding. A clot can travel in the bloodstream before being deposited in an organ or limb.

Deep vein thrombosis (DVT), a blood clot in the deep veins of your leg, is one of the main causes of pulmonary embolisms.


A fracture to a long bone, such as a thigh bone, can lead to fat particles within the bone being released into the bloodstream. They can also sometimes develop following severe burns or as a complication of bone surgery.


Embolisms can also occur if air bubbles or other gases enter the bloodstream.

Air embolisms are a particular concern for scuba divers. If a diver swims to the surface too quickly, the change in pressure can cause nitrogen bubbles to develop in their bloodstream. This can cause decompression sickness, which is often referred to as "the bends".

Read more information about an air embolism.


In people with severe atherosclerosis (narrowed arteries due to a build-up of cholesterol), small pieces of cholesterol can sometimes break away from the side of a blood vessel, resulting in an embolism.

Amniotic fluid

In rare cases, amniotic fluid – which surrounds and protects a baby inside the womb – can leak into the mother's blood vessels during labour, causing a blockage. This could lead to breathing problems, a drop in blood pressure and loss of consciousness.

Increased risk

Your risk of an embolism is increased by:

Treating embolisms

How an embolism is treated will depend on:

  • what caused the blockage
  • the size of the blockage
  • where in the body the blockage is

A surgical procedure called an embolectomy is sometimes carried out to remove an obstruction. During this operation, the surgeon will make a cut in the affected artery and the foreign body causing the blockage will be sucked out in a process known as aspiration.

Medication may be used to dissolve embolisms (thrombolysis) caused by blood clots. Anticoagulant medication, such as warfarin, heparin and low-dose aspirin, can help make the blood less sticky and stop further clots forming.

Embolisms caused by air bubbles are usually treated in a hyperbaric chamber. The air pressure inside the chamber is higher than the normal air pressure outside, which helps reduce the size of the air bubbles inside the diver's body.

Read more about treating air embolisms.


It's not possible to prevent all embolisms, but you can take steps to significantly reduce your risk. These steps include:

  • eating a healthy diet – low in fat, high in fibre and including whole grains and plenty of fresh fruit and vegetables (at least five portions a day)
  • limiting the amount of salt in your diet to no more than 6g (0.2oz or 1 teaspoon) a day
  • losing weight if you're overweight or obese, using a combination of regular exercise and a calorie-controlled diet
  • stopping smoking, if you smoke
  • exercising for a minimum of 150 minutes a week

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